I don’t know this, but have you tried standard CSS comma separation? Atom kinda uses CSS-like syntax but I’m not sure exactly where the similarities end. But yeah, try '.source.php, .source.scss' as your ‘selector’. I doubt it’ll work though.

As for your bonus question, I don’t know why that wouldn’t work (other than indentation but presumably you’ve triple-checked that) but the code you pasted here ends in a backtick (``` ``) rather than a single quote. That may be a copy-pase error or it may be the source of your issue.